A now considerable literature has emerged on the regime type which O'Donnell labeled ,9 both in terms of its origins and the policies which typify its development.' While discussion of the end of all such regimes is premature, individual cases today appear to be subject to great challenges. The purpose of the present essay is to offer a coherent explanation as to when individual bureaucratic-authoritarian governments will be most vulnerable to collapse. To narrow the focus some, analysis will concentrate only on the four cases of exclusionary bureaucratic-authoritarianism still in power-Brazil since 1964, Chile and Uruguay since 1973, and Argentina (in its most recent version) since 1976.2 Three particular aspects of the problem will be singled out for special attention: (1) the bases of legitimacy in bureaucratic-authoritarian regimes; (2) the likelihood of regime institutionalization; and (3) the possibilities for the emergence of opposition, culminating in the creation of an alternative regime in power. What follows falls into two main sections plus a brief conclusion. The first is a synthesis of much of the existing writing as it relates to the three major concepts chosen for examination. As will be made clear, the new military regimes have sought to replace democratic governments with authoritarian rule supposedly legitimated by a restored sense of political and social order and by a renewal of economic growth. Successful economic development, in turn, is expected to create the necessary popular support among a minority for the restructuring of the political system, eventually allowing for reduced levels of repression as the new regime gains hegemonic control. The opposition that will emerge will be highly restricted and will in no sense challenge the regime. The second section compares the realities of the present with the new authoritarian wishes. What is stressed is the effects of serious economic problems in undermining the military's self-defined base of legitimacy and, with this change, in weakening its willingness to use repression to control dissension. Where military commitment to long-term praetorian rule is less than total and/or a plausible, not highly threatening civilian alternative exists, the effects of economic crisis have been to encourage an at least temporary military exit. Even where those in charge are determined to retain power at all costs, the increasingly catastrophic state of the economy is producing major divisions among the officers and less consistent